Ribbon anodes

Figure 7.12 (a) Ribbon anodes being applied to the underside of a jetty in Jersey. 

Certain areas of the soffit, beams and all of the columns plus support trestles were protected using ribbon anodes.The tide rises to near soffit level and there is an Mm tidal range, (b) 55-57 St Martin s Lane London showing the front 2 zones on a brick building with steel columns after installation of ribbon anode system the reference electrode locations are indicated by Zl Rl, etc. 

Ribbon anodes are also increasingly popular on historic steel framed masonry or brick clad structures where they can be fitted in the mortar joints (see Figure 7.12(b)). 

The anode system may be a single component, such as flame sprayed zinc, or multiple component such as a titanium mesh with a cementitious overlay. It may consist of a single continuous anode such as mesh or coatings, or multiple anodes connected together such as ribbon anodes or the discrete rod anodes. All anodes require electrical connections to the power supply. As for the rebar connections these should be duplicated for redundancy. 

In recent years, continuous zinc ribbon anodes have been used in a variety of underground applications (Kurr, 1973 Peabody, 1976 O Connell, 1977). This type of product has broadened the applications for zinc anodes, for it provides small increments of current continuously along the entire length of a cathode. Its uses are generally considered to lie in specialty applications, where other methods of cathodic protection are either impractical or extremely costly (see later section on induced ac on pipelines). Bagnulo (1973, 1984) has developed a tape with an electrically conducting adhesive as described in the Mechanical Coatings part of Chapter 1. 

Fig. 4,6 Zinc continuous ribbon anode to steel current output versus resistivity (Kurr, 1979).

Kurr, G. W. (1967). Sacrificial zinc ribbon anodes. Mater. Prot., 6(4), 30-33. 

Krishnamurthy et al. (1988 b) found significant refinement of microstructure in rapidly solidified alloys, with the maximum refinement occurring near the quenched surface of the ribbons. Anodic polarization of the ribbon showed a pseudo-passivation effect which led to a significantly lower current density. Hehmann et al. (1989) compared the corrosion of rapidly solidified Mg-Al alloys containing 10-24% Al in aerated 0.001 M NaCl solution with that of chill-cast alloys of the same composition. Electrochemical characterization revealed a... 

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

The high driving voltage may, however, result in overprotection. Combined with relatively poor capacity (1 230Ah/kg) and high unit cost these disadvantages mean that magnesium rarely finds application in subsea environments where alternatives are available. Despite this, Mg-Al-Zn anodes have been used in seabed mud and for rapid polarisation of structures (in ribbon form). 

As the general standard of protective coatings has improved (materials, application and construction standards) the use of sacrificial anodes has extended to soil of ca. 10 000 ohm cm or more for buried pipelines. By using anodes in extruded ribbon form and placing them as close as possible to the structure to be protected they can be used in soils of high resistivity. 

Imai H, Takei Y, Shimizu K, Matsuda M, Hirashima H (1999) Direct preparation of anatase Ti02 nanotubes in porous alumina membranes. J Mater Chem 9 2971-2972 Michailowski A, A1 Mawlawi D, Cheng GS, Moskovits M (2001) Highly regular anatase nanotubule arrays fabricated in porous anodic templates. Chem Phys Lett 349 1-5 Jung JH, Kobayashi H, van Bommel KJC, Shinkai S, Shimizu T (2002) Creation of novel helical ribbon and double-layered nanotube Ti02 structures using an... 

Galvoline [Dow], TM for a cored magnesium ribbon used as a continuous anode for the cathode protection of buried pipelines and other metal structures. Combustible. 

The demands of practical applications led to attempts to overcome the high electric resistance of thin ribbons by a new technical solution of laser-induced surface vitrification (105, 106). First an amorphous alloy ribbon was adhered uniformly to a nickel plate by heat treatment. Subsequently, this surface alloy layer was transformed to the amorphous structure by laser surface melting and self-quenching (107). A sample consisting of Pd56Rh23P oSi9 adhered to bulk crystalline nickel exhibited anodic characteristics very similar to those of the melt-spun amorphous ribbon (102). Clearly, similar improvements forced by practical demands will be a part of the future use of amorphous alloys. 

Soil Clay, particulate, oil, grease Surface Painted, anodized aluminum Application Method Spray/brush/wipe Manufacture Ribbon or paddle blender Composition A % Wt... 

This anode consists of an expanded titanium mesh with a catalytic mixed metal oxide coating. The anode is fixed to the concrete surface and then overlaid with concrete. This is usually dry spray shotcrete on vertical and soffit surfaces or cast on top surfaces and decks. It is also available in a number of mesh sizes and as a ribbon (described separately). 

This anode system is one of the most durable and can be applied in any condition from underground and underwater to dry atmospheric exposure. It is also widely used on buildings with steel frames behind brick or stone facades where the ribbon can be inserted in the mortar joints as shown in Figure 7.12(b). 

The NACE Standard test method for testing embeddable impressed current anodes applies to this anode. TM0294-2004. Testing of embeddable impressed current anodes for use in cathodic protection of atmospherically exposed steel-reinforced concrete. This was developed to assess the performance of the coated titanium equivalent to a 40 year life. It does not test the grout that the ribbon is embedded in. 

This is a wet sprayed mortar containing nickel plated carbon fibres to achieve conductivity (Figure 7.14). It requires a primary anode, usually the titanium mesh ribbon. This is a proprietary anode and there are no variations. 

As stated in the anode descriptions earlier, there are also two NACE test methods for cathodic protection anodes. These are TM 0294 on embeddable anodes (mixed metal oxide coated titanium, mesh, ribbon, tnbes, rods and conductive ceramic tubes) and TMO1105-2005 on organic-based condnc-tive coating anodes. In addition there is a specification for applying thermal sprayed zinc anodes to concrete American Welding Society (2002). 

Dead load or clearance problems Difficult Difficult (needs overlay) Ok Ribbon, probe anodes or soffit anode Ok Ok Overlays add dead weight and cut clearance... 

If cathodic protection is the chosen rehabilitation methodology then the correct choice of anode is vital. For non-marine applications the usual choice will be an impressed current system. If it is a wearing surface then coatings are usually excluded. This leads to the use of the conductive concrete anode or one of the titanium configurations in an overlay or titanium ribbons in slots. 

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